Studies are being performed to elucidate the mechanisms by which the active sliding between flagellar tubules is controlled and coordinated to produce the planar bending waves characteristic of sperm flagella, and to clarify how the dynein arms interact with the axonemal structure and with ATP to produce active sliding between tubules. Analysis of the asymmetrical beating produced by Ca 2 ions has shown that it appears to be the result of the propagation of symmetrical bending waves along a flagellum whose "rest position" is curved into a nearly circular arc. Electron microscopic studies are being done to determine the subunit structure of the dynein arms. The bending and straightening of flagella in which oscillatory beating is inhibited with vanadate, decreased pH, or Ca 2 ions are being studied to determine the factors that regulate the activity of dynein cross-bridges at different positions along the flagellum, as well as about the properties of the structural components that resist sliding and convert it into bending.